The "real" device gives you what it measures as your real highs and lows while the OTC devices won't report high highs or low lows.
I have a Stelo (I was curious and diabetes runs in my family) while my wife has the Dexcom.
https://navid200.github.io/xDrip/docs/Dexcom/G7.html
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It also probably gives the companies really valuable data.
The "real" device gives you what it measures as your real highs and lows while the OTC devices won't report high highs or low lows.
I have a Stelo (I was curious and diabetes runs in my family) while my wife has the Dexcom.